1. Field
The present invention relates to a light emitting diode and a method of fabricating the same, and more particularly, to a light emitting diode having an interlayer with high dislocation density and a method of fabricating the same.
2. Discussion of the Background
Generally, gallium nitride-based compound semiconductors such as gallium nitride (GaN), aluminum nitride (AlN), indium gallium nitride (InGaN), or the like, have a direct transition type energy band structure having excellent thermal stability, which have recently been in the limelight as materials for blue and ultraviolet light emitting diode. In particular, the indium gallium nitride compound semiconductor has been of great interest due to a narrow bandgap. The light emitting diode using the gallium nitride-based compound semiconductor has been used in various applications, such as a large-scale color flat panel device, a signal lamp, interior lighting, a high density light source, a high-resolution output system, optical communications, and the like.
A nitride semiconductor layer of III-group elements is grown on a heterogeneous substrate of sapphire or silicon carbide (SiC) having a hexagonal structure, or the like, by a process of a metal organic chemical vapor deposition method (MOCVD), or the like. However, when the nitride semiconductor layer of III-group elements is formed on the heterogeneous substrate, cracks or dislocations occur within the semiconductor layer due to a difference of a lattice constant and a thermal expansion coefficient between the semiconductor layer and the substrate.
The cracks or dislocations occurring within the semiconductor layer, in particular, an active layer or layers adjacent thereto aggravate characteristics of the light emitting diode. Therefore, in order to mitigate a stress caused by a difference in the lattice constant and the thermal expansion coefficient between the substrate and the semiconductor layer, a buffer layer is generally used.
FIG. 1 is a cross-sectional view for describing a method of fabricating a gallium nitride-based light emitting diode according to the related art.
Referring to FIG. 1, a buffer layer 13 is formed on the substrate 11. The buffer layer 13 is generally made of AlxGa1-xN (0≦x≦1) at a temperature of 400 to 600° C. by using the MOCVD process, or the like. Then, a lower semiconductor layer 15 is formed on the buffer layer 13. The lower semiconductor layer 15 is generally formed of a GaN layer at a temperature of 900 to 1200° C. An n-type GaN contact layer 17, an active layer 19, and a p-type GaN contact layer 21 are formed thereon.
According to the related art, the buffer layer 13 and the lower semiconductor layer 15 may be formed between the n-type contact layer 17 and the substrate 11 to reduce the occurrence of cracks or dislocations, or the like, caused by the differences in the lattice constant and the thermal expansion coefficient between the substrate 11 and the n-type contact layer 17.
However, despite the adaptation of the buffer layer 13 and the lower semiconductor layer 15, a crystal defect density within the active layer 19 is still high. In particular, the dislocation generated in the buffer layer 13 is transferred to the active layer 19 through the lower semiconductor layer 15 and the n-type contact layer 17 to reduce luminous efficiency of the light emitting diode. In addition, the dislocations are transferred to the p-type contact layer to aggravate electro-static discharge characteristics of the light emitting diode.
Meanwhile, in order to prevent the dislocations generated from the lower semiconductor layer from being transferred to an upper semiconductor layer, an interlayer having a supper-lattice structure may be adopted. The interlayer having the super-lattice structure is formed by alternately growing super thin layers of different compositions, thereby cutting off the dislocation and improving crystallinity of the semiconductor layer formed thereon.
However, in order to form the interlayer having the super-lattice structure, temperature, pressure, and source gas flow of a growth chamber need to be alternately controlled under conditions that each layer is suitably grown within the super-lattice structure. Therefore, an excessive process time to grow the interlayer having the super-lattice structure is required, which excessively increases the process time and the process costs required to fabricating the light emitting diode.